PNIVERSITY  OF  CALIFORNIA  PUBLICATIONS 

COLLEGE  OE  AGRICULTURE 

AGRICULTURAL  EXPERIMENT  STATION 

BERKELEY,  CALIFORNIA 


PEAR  POLLINATION 


BY 
WARREN  P.  TUFTS  AND  GUY  L.  PHILP 


BULLETIN  No.  373 

December,  1923 


UNIVERSITY  OF  CALIFORNIA  PRINTING  OFFICE 

BERKELEY,  CALIFORNIA 

1923 


Digitized  by  the  Internet  Archive 

in  2012  with  funding  from 

University  of  California,  Davis  Libraries 


http://www.archive.org/details/pearpollination373tuft 


PEAR  POLLINATION 

By  WAEREN  P.  TUFTS  and  GUY  L.  PHILP 


Whether  the  Bartlett  and  other  leading  varieties  of  pears  require 
or  are  benefited  by  cross-pollination  is  a  question  which  is  arousing 
increasing  interest  on  the  part  of  pear  growers,  especially  since  the 
publication  of  a  preliminary  report  on  pear  pollination.1  This  report 
being  now  out  of  print,  it  seems  desirable  to  present  at  this  time  all 
the  data  available  regarding  the  pollination  requirements  of  the 
different  pear  varieties  grown  in  California. 

The  fact  that  Bartlett  trees,  planted  without  any  regard  to  cross- 
pollination,  have  yielded  profitable  crops  under  valley  conditions,  has 
led  some  to  believe  that  this  variety  is  self -fertile.  On  the  other  hand, 
these  same  growers  have  noticed  when  they  have  a  stray  tree  of  some 
other  variety  in  their  orchard  that  the  surrounding  Bartletts  are  more 
fruitful  than  the  remainder  of  the  orchard.  This  seems  to  indicate 
that  the  Bartlett,  under  valley  conditions,  is  benefited  by  cross- 
pollination.  In  the  Sierra  Nevada  foothills,  thoughtful  and  observant 
growers  have  felt  sure  that  the  Bartlett,  under  their  conditions,  is 
always  self -sterile.  With  the  increased  plantings  of  pear  varieties 
other  than  Bartlett  under  both  valley  and  foothill  conditions,  the 
pollination  question  assumes  a  still  greater  importance. 

Waite2  discovered  about  thirty  years  ago  that  the  Kieffer  pear,  a 
leading  variety  of  the  eastern  and  middle  states,  is  practically  self- 
sterile.  Since  that  time  there  has  been  much  discussion  throughout 
the  country  as  to  whether  or  not  certain  varieties  other  than  the 
Kieffer  could  be  benefited  by  cross-pollination  and,  if  so,  what  varieties 
could  be  depended  upon  to  serve  as  pollinators. 

Fletcher3  states  that:  "The  results  of  hand-pollinating  8408  Kieffer 
pear  blossoms  and  9867  Bartlett  pear  blossoms  in  the  years  1903,  1906, 
and  1907  indicate: 

"1.  In  West  Virginia  and  Michigan,  and  probably  in  other  parts 
of  the  east,  unsatisfactory  results  may  be  expected  from  planting 
either  Bartlett  or  Kieffer  in  large  blocks  so  that  cross-pollination  by 
insects  is  not  general. 

i  Tufts,  W.  P.,  Pollination  of  the  Bartlett  Pear,  Calif.  Agr.  Exp.  Sta.  Bull. 
No.  307,  May,  1919. 

2  Waite,  M.  B.,  Pollination  of  Pear  Flowers,  Bull.  5,  Div.  Veg.  Path.,  U.S. 
Dept.  Agr.,  1894. 

3  Fletcher,  S.  W.,  Report  of  Va.  Agr.  Exp.  Sta.,  1909-1910. 


4  UNIVERSITY    OF    CALIFORNIA EXPERIMENT    STATION 

"2.  Anjou,  Lawrence,  Duchess,  and  Kieffer  are  satisfactory  varie- 
ties for  planting  with  Bartlett,  so  far  as  pollination  is  concerned. 
Some  years  the  Kieffer  does  not  blossom  simultaneously  with  Bartlett, 
but  usually  the  blossoming  seasons  overlap  sufficiently." 

Kraus4  advises  planting  Clairgeau,  Anjou,  Howell,  or  Kieffer  with 
Bartlett  for  the  purpose  of  affecting  cross-pollination. 

Wisker5  says  that:  "California's  pear  profits  would  be  greater  if 
some  other  variety  were  planted  with  Bartlett  for  cross-pollination. 
Anjou,  Bosc,  and  Cornice  are  good  pollinators  and  sell  for  higher 
prices  than  Bartlett.  We  have  increased  the  fruitfulness  of  an  old 
Bartlett  orchard  more  than  200  per  cent  by  inter -grafting  other 
varieties. ' ' 

Weldon0  believes  that:  "The  best  results  in  growing  Bartlett  pears 
cannot  be  attained  unless  other  varieties  are  planted  with  them  in  the 
orchard.  Despite  the  evidence  that  this  should  be  done,  there  are 
thousands  of  acres  of  Bartletts  being  planted  in  California  each 
season  with  utter  disregard  of  the  benefits  that  might  be  derived  by 
planting  one  or  more  varieties  for  cross-pollination.  In  certain  new 
pear-growing  sections,  the  writers  have  recently  seen  thousands  of 
acres  of  Bartletts  in  blocks  of  five  acres  to  more  than  one  hundred 
acres  each,  with  no  other  varieties  near,  except  possibly  an  occasional 
tree  of  some  favorite  pear  planted  for  home  use. 

"In  some  of  these  sections  heavy  winds  and  extremes  of  heat  and 
cold  occur,  making  more  necessary  the  strictest  attention  to  every 
detail  that  would  tend  to  increase  productivity.  The  fruit  in  general 
is  good,  and  the  trees  everywhere  have  done  well.  So  far  as  it  has 
been  possible  to  determine,  they  are  self -fertile  to  a  remarkable  degree 
when  the  existing  conditions  are  taken  into  consideration,  but  it  is 
safe  to  predict  that  there  will  be  years  of  short  crops  because  of  the 
absence  of  other  pears,  and  the  average  production  of  these  sections 
throughout  a  series  of  years  will  be  far  below  what  it  would  be  with 
other  varieties  planted  along  with  the  Bartletts  for  cross-pollination 
purposes.  There  are  older  pear  growing  sections  of  the  state  where 
large  areas  of  Bartletts  have  been  planted  by  themselves  and  where 
the  same  arguments  against  the  practice  may  be  used." 

Although  practically  all  writers  agree  in  advising  the  inter-plant- 
ing of  other  varieties  to  pollinate  the  Bartlett,  even  in  the  valley 
locations  in  Cilifornia,  nevertheless  the  bulk  of  the  acreage  planted 

i  Kraus,  E.  J.,  The  Pollination  Question,  Ore.  Agr.  Exp.  Sta.  Cire.  Bull.  No. 
20,  1912. 

•>  Wisker,  A.  L.,  Price  List  Loma  Rica  Nurseries,  1915-1916. 

(i  Weldon,  G.  P.,  Pear  Growing  in  California,  Calif.  State  Com.  of  Hort., 
p.  234,  1918. 


Bulletin  373]  PEAR  POLLINATION  5 

to  Bartlett  in  the  state  contains  no  other  variety.  The  authors  of  this 
paper  outlined  and  performed  certain  experiments  during  the  seasons 
of  1916,  1917,  1918,  1919,  1920,  1922,  and  1923  designed  to  test  the 
accuracy  of  the  observations  enumerated  above. 

PKOBLEMS  OF  PEAK  POLLINATION 

Inasmuch  as  the  Bartlett  is  the  pear  of  greatest  commercial  value 
in  California,  more  attention  in  these  experiments  has  been  given  to 
this  variety  than  to  others.  The  increasing  interest  of  pear  growers 
in  varieties  other  than  the  Bartlett  has  resulted  in  the  collection  of 
some  data  with  regard  to  the  pollination  requirements  of  certain  of 
these  sorts. 

In  planning  the  work,  of  which  this  bulletin  is  a  report  the  writers 
have  had  in  mind  the  differ ences  of  altitude,  climate,  and  soil,  exist- 
ing in  foothill,  valley,  and  coastal  regions  in  California,  and  have 
attempted  to  secure  at  least  a  partial  solution  of  the  following  problems 
for  these  various  conditions. 

1.  Will  pears  when  planted  in  solid  blocks  be  commercially  profit- 
able without  pollinizers?  If  found  to  be  profitable  under  these  con- 
ditions, these  varieties  may  be  termed  self -fertile:  if  unprofitable,  they 
should  be  termed  self -sterile.1 

2.  If  pears  will  not,  under  all  conditions,  produce  profitably  in 
the  absence  of  cross-pollination,  what  varieties  should  be  used  as 
pollinizers?    This  is  a  question  of  inter-fertility. 

3.  If  it  should  be  found  that  by  inter-planting,  the  yield  per  tree 
can  be  increased,  will  the  increase  per  acre  make  inter-planting  com- 
mercially  profitable? 

4.  Even  though  two  varieties  may  pollinate  each  other,  it  is 
important  that  the  following  points  should  always  be  considered  in 
selecting  pollinizers : 

a.  Commercial  value  of  the  pollinizer. 

b.  Coincidence  of  bloom  of  the  pollinizer  with  that   of  the 

variety  to  be  pollinated. 

c.  Succession  of  ripening  of  the  varieties,  for  convenience  in 

harvesting. 

d.  Amount  of  pollen  produced  by  the  pollinizer. 

e.  Germinability  of  the  pollen  produced  by  the  pollinizer. 

7  The  writers  prefer  the  terms  "barren"  and  "fruitful"  as  explained  by 
Kraus  in  the  Journal  of  Heredity,  vol.  6,  no.  12.  pp.  549-557,  rather  than  the 
inexact  terms,  "sterile"  and  "fertile."  The  latter  terms  have  been  used  in 
this  paper  on  account  of  the  fact  that  the  general  public  is  more  or  less 
familiar  with  these  expressions. 


UNIVERSITY   OF   CALIFORNIA — EXPERIMENT   STATION 


Bulletin  373] 


PEAR    POLLINATION 


OEGANIZATION  OF  THE  WOKK 

The  methods  employed  for  investigating  the  problems  just  out- 
lined were  those  commonly  in  use  in  cross-pollination  experiments. 
Briefly  stated,  this  consisted  of  removing  the  stamens,  the  pollen- 
bearing  organs,  from  the  flowers  to  be  pollinated  (fig.  1)  and  then 
applying  the  desired  kinds  of  pollen  by  hand.  Accurate  counts  of 
the  hand  pollinated  flowers  were  made  and  recorded.  The  fruits 
resulting  from  these  artificial  pollinations  were  counted  and  the  proper 
records  made  after  the  June  drop  and  again  at  harvest. 


Average  Blossoming  Pates  or  Certain  Pear  Varieties 

V//sivER5iTy  Farm -Pavis, California-  614  TO  I923~Lngl 


Le  Go/ite 
Ale/scon 
Kiept-er 
No/cell 

fORELLE 

a^govle/ie 
Glairgeav 
Easter 
P.JiovEy 

PDARRy 

GlovtMorcEav 

Wl/HTER  T^LIS 
BARTLETT 

BLOOPGOOP 
OAtlCE 
A/MJOV 

B.5.POX 

GlFEORP 

Comet 

Seckel 

hARpy 

Glapp  Favorite 

COL.WlLPtR 
B05C 


y£AR5 

averagep 

9 
8 
9 
9 


MARCH 

APRIL 

i  ■  m  i  r-  mm  1 1  ■  ■ 

MiBi^-fifT-fl 

r 

PE5IGNAT  E5 

BEGIMLMG 

or-  PULL 

Bloom 


Fig.  2. — The  average  dates  of  first,  last,  and  full  bloom  of  certain  pear 
varieties  covering  a  period  of  four  to  ten  years.  The  number  of  years  averaged 
is  shown  in  a  separate  column. 


During  the  seasons  of  1916,  1917,  1920,  and  1923.  experiments  were 
conducted  in  the  University  Farm  orchards  at  Davis,  where  typical 
Sacramento  Valley  conditions  prevail.  The  trees  are,  at  this  writing, 
fourteen  years  old  and  are  in  an  excellent  state  of  vigor.  In  1918  and 
1919  experiments  were  conducted  in  the  Vaca  Valley  Ranch  orchards 
of  the  Earl  Fruit  Company  at  Vacaville.  The  trees  are  in  full  bear- 
ing, and  are  growing  on  some  of  the  best  soils  in  the  valley.  During 
the  seasons  of  1918,  1919,  1922,  and  1923,  certain  experiments  were 
conducted  on  the  Loma  Rica  Ranch  at  Grass  Valley.  The  trees  in  the 
Loma  Rica  orchards  are  nine  years  old  and  are  making  a  moderate 
vegetative  growth.  This  orchard  is  planted  on  typical  red  soil  of  the 
Sierra  Nevada  foothills  at  3000  feet  elevation.  In  1920,  experiments 
were  conducted  in  the  Santa  Clara  Valley,  in  the  Keeble,  Wilcox,  and 


8  UNIVERSITY    OF    CALIFORNIA EXPERIMENT    STATION 

McCurdy  orchards.  The  trees  in  these  latter  orchards  are  in  full 
bearing  and  in  good  condition.  Several  crosses  were  made  in  1922  in 
the  Searby  orchard  in  the  Occidental  district  of  Sonoma  County. 
Here  the  trees  are  healthy  and  in  full  bearing. 

THE  BLOOMING  PERIOD  OF  CERTAIN  PEAR  VARIETIES 

Figure  2  (p.  7)  shows  the  average  dates  of  the  first,  last,  and 
full  bloom  of  twenty-five  pear  varieties,  as  grown  at  the  University 
Farm,  Davis,  for  the  years  1914  to  1923  inclusive  (unless  otherwise 
noted).  Attention  is  called  to  the  fact  that  the  blooming  period  of 
the  Bartlett  is  considerably  longer  than  that  of  any  other  variety 
included  in  these  studies.  A  careful  study  of  these  data  as  well  as 
those  presented  b}^  Weldon,8  including  the  blooming  dates  of  nearly 
sixty  varieties,  leads  to  the  conclusion  that,  with  the  possible  excep- 
tion of  a  few  very  early  blooming  sorts  such  as  the  LeConte,  Forelle, 
Kieffer,  and  Clairgeau,  the  blooming  period  of  the  Bartlett  coincides 
very  well  with  that  of  practically  all  other  important  varieties.  Even 
the  very  early  blooming  varieties  just  mentioned  do  not,  on  the 
average,  reach  the  height  of  their  bloom  many  days  before  the  Bartlett, 
and  in  most  years  their  blooming  periods  overlap  sufficiently  to  make 
them  available  as  pollinators. 

PRODUCTIVENESS  AND  VIABILITY  OF  POLLEN  USED 

In  seven  years'  tests,  there  have  been  only  three  cases  where  pollen 
failed  to  give  a  satisfactory  artificial  germination.  These  were  Blood- 
good  and  Seckel  in  the  year  1920  and  Surprise  in  1923.  In  the  case 
of  Seckel,  the  self-pollinated  flowers  produced  a  three  per  cent  set, 
indicating  a  partial  germination  under  natural  conditions.  No  reason 
can  be  given  for  the  failure  of  the  other  two  varieties  of  pollen  to 
germinate  artificially. 

Pear  pollen,  on  the  average,  does  not  give  as  high  germination 
tests  as  some  of  the  other  fruits,  although  a  sufficient  number  of  the 
pollen  grains  germinate  to  insure  thorough  pollination  whenever  the 
pollen  is  applied  artificially. 

In  selecting  a  pollinizer  for  his  commercial  orchard,  the  grower 
must  take  into  consideration  not  only  whether  the  pollen  produced  by 
a  certain  variety  is  viable,  but  also  whether  the  variety  selected  is  a 
good  pollen  producer.  Fortunately  all  varieties  tested  have  proved 
to  be  abundant  pollen  producers.  Table  1  gives  the  average  artificial 
germination  of  the  different  varieties  used. 

s  Weldon,   G.  P..  Pear  Growing  in   California,   Calif.   State   Com.   of  Hort., 


Bulletin  373] 


PEAR   POLLINATION 


TABLE   1 

Germinability  of  Pollen 

Percentage  germination  in  a  12  per  cent  cane  sugar  solution 

Seasons  1916  to  1923;  inclusive 


Variety 

Source 

1916 

1917 

1918 

1919 

1920 

1922 

1923 

Alencon 

Univ.  Farm 

63 

26 

9 
33 

22 
45 

26 
63 

21 

41 
36 

32 

76 
42 
19 

74 
43 

58 
39 

25 

45 
36 

44 

8 
26 

16 
22 

24 
21 

35 
29 

15 

6 

23 
25 

6 

29 

20.3 

12 
22 

41 
80 
75 

62 

0 

62 

22 

82 

54 
46 

36 

58 
40 

44 

45 

21 
17 
30 
17 
33 
17 

55 

38 

18 
0 

28 
11 
36 
21 
35 

10 

40 

20 
73 

58 
80 

30 

18 

5 
15 

82 
85 

15 
44 

18 

18 

8 

37 

10 

31 
31 
20 

45 

18 

19 

42 

58 

13 
15 
19 
63 

27 
38 

70 

36 
15 
17 

33.6 

Anjou 

Univ.  Farm 

Anjou . .. 

Grass  Valley 

Angouleme 

Univ.  Farm 

Bartlett 

Univ.  Farm 

62 

Bartlett. 

Grass  Valley 

31 

Bartlett 

Vaca  Valley 

Bartlett 

Sonoma  Co...  . 

Bartlett 

Santa  Clara  (Mc)  .... 
Univ.  Farm 

Bloodgood 

Bloodgood 

Santa  Clara  (W) 

Univ.  Farm 

Bosc 

Bosc 

Grass  Valley 

21 

Clairgeau 

Univ.  Farm 

69 

Clairgeau 

Grass  Valley 

Clairgeau 

Santa  Clara  (K) 

Univ.  Farm 

Clapp  Favorite.. .. 

88 

Col.  Wilder 

Univ.  Farm 

35 

Cornice 

Univ.  Farm 

73 

Cornice 

Grass  Valley 

13 

Cornice 

Santa  Clara  (K) 

Univ.  Farm 

Dana  Hovey 

88 

Dana  Hovev 

Grass  Valley 

Easter 

Univ.  Farm 

52 

Easter 

Grass  Valley 

Easter 

Santa  Clara  (Mc)  .... 
Univ.  Farm 

Flemish  Beauty.... 
Forelle 

Univ.  Farm 

90 

Forelle.... 

Grass  Valley 

Gifford 

Univ.  Farm 

G.  Morceau 

Univ.  Farm 

G.  Morceau 

Santa  Clara  (Mc)  .... 
Univ.  Farm 

Hardy 

Hardy 

Santa  Clara  (K) 

Univ.  Farm 

Howell 

Howell 

Grass  Valley 

Howell 

Santa  Clara  (S) 

Univ.  Farm 

Kieffer 

Le  Conte.... 

Univ.  Farm 

Lincoln  ... 

Grass  Valley 

Madeline 

Univ.  Farm 

Patrick  Barry 

Patrick  Barry 

Seckel 

Univ.  Farm 

91 

Grass  Valley 

Univ.  Farm 

87 

Seckel 

Grass  Valley 

Surprise 

Univ.  Farm 

0 

W.  Bartlett .. . 

Grass  Valley 

W.  Nelis..  . 

Univ.  Farm 

44 

W.  Nelis  . 

Grass  Valley 

11 

W.  Nelis 

Santa  Clara  (Mc)  .... 

Santa  Clara  (Mc)  .... 

Average 

W.  Seckel 

57 

Mc,  McCurdy  orchard;  K,  Keeble  orchard;  W,  Wilcox  orchard;  S,  Smith  orchard — all  in  the  Santa 
Clara  Valley. 


10  UNIVERSITY    OF    CALIFORNIA — EXPERIMENT   STATION 

RELATION  OF  NORMAL  SET  TO  FINAL  CROP 

Immediately  after  the  petals  fall,  each  flower  begins  to  form  a 
fruit.  During  the  following  two  or  three  weeks  a  certain  percentage 
of  these  young  fruits,  for  reasons  not  fully  understood,  drop  off, 
leaving  only  a  rather  low  percentage  of  the  total  number  of  original 
blossoms  to  continue  development.  It  is  quite  necessary  that  this  drop 
take  place,  as  the  tree  under  average  circumstances  would  never  be 
able  to  carry  so  many  fruits  through  to  maturity.  Just  what  factors 
determine  which  of  these  young  fruit  shall  drop  is  not  at  present 
known.  Later  in  the  season  there  takes  place  still  another  falling  of 
the  young  fruits  known  as  the  "June  drop." 

The  expression  normal  set  is  a  more  or  less  technical  way  of 
designating  the  percentage  of  fruit  which  the  tree  sets  under  normal 
conditions  when  left  open  to  insect  pollination.  It  is  obvious  that 
the  normal  set  may  be  determined  at  any  time  up  to  the  end  of  the 
season  by  counting  the  fruits  on  a  tree  and  comparing  the  number 
with  the  original  bloom.  In  these  experiments,  approximately  2000 
blossoms  of  each  variety,  well  distributed  over  the  trees,  were  counted 
each  year  and  proper  records  kept  to  determine  the  normal  set  after 
the  first  drop,  after  the  second  drop,  and  at  harvest  time. 

The  questions  at  once  arise  as  to  what  percentage  of  normal  set  at 
harvest  time  constitutes  a  full  crop,  and  what  is  meant  by  a  "full 
crop."  What  constitutes  a  full  crop  of  any  fruit  is  perhaps  largely 
a  question  of  opinion,  judgment,  or  guess.  It  varies  with  such  factors 
as  variety,  soil,  and  moisture  conditions.  What  would  be  considered 
a  full  crop  under  foothill  conditions  would  not  necessarily  be  the 
same  in  a  valley  location. 

Table  2  casts  some  light  upon  the  question  as  it  shows  the  normal 
set  of  the  Anjou,  Hardy,  Clairgeau,  Flemish  Beauty,  and  Forelle  in 
1922,  as  grown  under  conditions  existing  in  the  University  Farm 
orchards.  The  average  yield  of  these  trees  has  been  reduced  to  an 
acreage  basis.  The  trees  under  observation  were  planted  during  the 
spring  of  1912,  being  twenty-four  feet  apart  by  the  square  system, 
which  gives  approximately  seventy-five  trees  to  the  acre.  Since  plant- 
ing, these  trees  have  received  good  commercial  care.  All  figures  are 
based  on  pears  harvested. 

An  examination  of  the  figures  presented  in  table  2  shows  that  too 
much  emphasis  must  not  be  placed  on  mere  percentages.  It  will  be 
noted  that  the  normal  set  for  Hardy  was  only  3.5  per  cent  with  a 
yield  of  12,550  pounds  of  fruit,  while  Flemish  Beauty  on  the  other 
hand,  had  a  normal  set  of  18.2  per  cent  with  practically  the  same 


Bulletin  373] 


PEAR   POLLINATION 


11 


yield.  Forelle,  with  a  normal  sot  of  25.2  per  cent,  produced  31,875 
pounds  of  fruit.  These  variations  in  yields  are  explained  by  the 
heavier  bloom  of  those  varieties  maturing  a  heavy  crop  with  only  a 
small  percentage  of  the  blossoms  setting. 

These  figures  are  presented  to  show  the  necessity  of  taking  the 
" normal  set"  counts  every  year  on  the  different  varieties  in  order  to 
secure  a  correct  basis  for  judging  results  of  artificial  pollination. 


TABLE  2 

Comparison  of  Normal  Set  with  Yield  in  Pounds  per  Acre 

University  Farm,  Davis,  1922 


Variety 


Per  cent 


Pounds 
per  acre 


Anjou 

Clairgeau 

Hardy 

Flemish  Beauty 
Forelle 


12,851 
21,600 
12,550 
12,075 
31,875 


POLLINATION  KEQUIEEMENTS   OF  THE  BAETLETT  PEAE 

A.  Interior  Valley  Conditions 

During  the  seasons  1916,  1917,  1920,  1922,  and  1923,  experiments 
were  conducted  in  the  University  Farm  orchards  at  Davis  for  the 
purpose  of  determining  whether  the  Bartlett  would  set  fruit  with  its 
own  pollen  under  Sacramento  Valley  conditions.  At  the  same  time 
numerous  crosses  were  made  on  the  Bartlett  to  find  the  best  pollenizers 
for  that  variety  (fig.  3).  The  results  of  this  work  are  summarized  in 
table  3. 

In  solidly  planted  Bartlett  orchards,  it  has  been  observed  that  in 
years  of  heavy  bloom  a  two  or  three  per  cent  set  from  the  self- 
pollinated  flowers  may  give  a  satisfactory  yield-  However,  in  the  long 
run,  experience  teaches  that  there  is  likely  to  be  many  years  of  light 
crops,  if  only  the  one  variety  is  planted. 

It  will  be  noted  from  a  study  of  table  3  that  self -pollinated  flowers 
gave  a  distinctly  lower  set  than  did  those  crossed  with  pollen  of  other 
varieties  except  in  the  case  of  Howell  in  1917  and  Anjou  in  1922. 
During  all  years  the  Bartlett  showed  evidence  of  self -sterility.  Of  the 
varieties  used  as  pollinizers  for  the  Bartlett,  Winter  Nelis  has  always 
given  the  highest  set  of  fruit.  The  writers  feel  that  under  average 
conditions  and  over  a  long  period  of  time  this  variety  should  be  given 


12 


UNIVERSITY    OF    CALIFORNIA EXPERIMENT    STATION 


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Bulletin  373] 


PEAR   POLLINATION 


13 


preference  as  a  pollinizer  for  the  Bartlett.  Cornice,  Bosc,  Easter,  and 
Hardy  also  have  given  satisfactory  results  and  are  recommended  in 
the  order  named.  Howell,  Angouleme,  Anjou,  and  Forelle  have 
likewise  been  fairly  satisfactory  as  pollinizers. 


BARTLETT  PEAR    POLLITNATIO/iS 

Interior  Valley  Locatjons~Vaca\6lley  l3l8.l9l9~\yni\A3rsitu.0rchards,l^isl9l6,l9IZ  I32I.I92Z.I923. 


Gross 

Formal  Set 
xSelt- 

xA/IGOVLEME 

xA/sjov 
xBosc 

xGoMICE. 

xEaster 
xHarpy 

xHoVYELL 
xWLnTER  /1EU5 


Percent  ot  Blossoms  Maturing 

1916  1919  \3Z\  I92Z 


■ 
1 

1 

1 

■ 

I 

■ 

1 

■ 

■ 
■ 

Fig.  3. — This  chart  shows  the  influence  of  various  kinds  of  pollen  when 
applied  to  the  flowers  of  the  Bartlett  pear  under  interior  valley  conditions. 
Note  the  comparatively  light  set  of  fruit  when  the  Bartlett  flowers  were  self- 
pollinated. 


B.  Coastal  Conditions 

The  work  under  coastal  conditions  was  done  in  1920  in  the  Santa 
Clara  Valley  and  in  1922  in  Sonoma  County.  The  results  of  this  work 
are  presented  in  table  4. 

A  study  of  table  4  shows  some  rather  interesting  results.  In  Santa 
Clara  Valley,  the  Wilcox  and  Mc Curdy  orchards  exhibited  a  wide 
difference  both  in  the  normal  set  and  self-pollination  tests.  In  the 
former  orchard,  the  Bartlett  was  practically  self-sterile,  while  in  the 
latter  it  was  self -fertile.  Also,  the  normal  set  in  the  Wilcox  orchard 
was  less  than  half  that  in  the  McCurdy  orchard.  Both  of  the  orchards 
ar?  considered  good  producers.  Possibly  the  differences  in  soil  can- 
ditions  and  cultural  treatments  may  be  responsible  for  the  seemingly 
conflicting  results  given  above. 

Cornice  and  Winter  Nelis  proved  to  be  the  best  pollinizers  for  the 
Bartlett,  while  Clairgeau  and  Easter  gave  only  fair  results;  Glout 
Morceau  and  Howell  proved  to  be  practically  inter- sterile  with  the 


14 


UNIVERSITY    OF    CALIFORNIA EXPERIMENT   STATION 


Bartlett.    Since  facilities  have  not  been  available  for  repeating  these 
experiments,  definite  conclusions  cannot  be  drawn  at  this  time. 

In  Sonoma  County,  the  only  work  attempted  was  self -pollinating 
the  Bartlett  and  crossing  that  variety  with  the  Winter  Nelis.  Weather 
conditions  were  not  favorable  for  the  setting  of  fruit  in  this  section 
in  1922,  but  while  the  percentage  set  was  small  the  crop  was  fairly 
satisfactory.  It  should  be  noted  that  while  the  Bartlett  was  to  a 
certain  degree  self-fertile,  the  set  was  materially  increased  by  using 
Winter  Nelis  as  a  pollinizer. 

TABLE  4 
Bartlett  Pear  Pollination  under  Coastal  Conditions 


1920 

1922 

Bartlett 

Number  of 
blossoms 
counted 

Per 
cent 
set 

Number  of 
blossoms 
counted 

Per 
cent 
set 

Normal  Set 

1980  Mc 
3718  W 
506  Mc 
549  W 
493  W 
524  W 
500  W 
504  W 
484  W 
548  W 

20.0 
9.8 

12.4 
0.5 
4.8 

24.2 
4.4 
0.4 
0.6 

23.5 

2013  S 
472  S 

451  S 

1  2 

Normal  Set 

xSelf 

2  5 

xSelf 

xClairgeau 

xComice 

xEaster 

xGlout  Morceau 

xHowell 

xWinter  Nelis 

5.3 

Note: — 1920.    Work  done  in  Santa  Clara  County.    Mc,  McCurdy  orchard;  W.  Wilcox  orchard. 
1922.    Work  done  in  the  Searby  orchard,  Sonoma  County. 


C.  Sierra  Nevada  Foothill  Conditions 

Pollination  experiments  were  conducted  in  the  Sierra  Nevada 
foothills  during  the  seasons  1918,  1919,  1922,  and  1923.  The  results 
of  this  work  are  presented  in  table  5. 

It  is  the  general  opinion  of  pear  growers  that  under  Sierra  Nevada 
foothill  conditions,  Bartlett  pears  must  be  cross-pollinated  to  produce 
satisfactory  crops.  A  study  of  table  5  indicates  this  to  be  the  case. 
During  three  of  the  four  years  that  these  experiments  were  in  progress, 
the  Bartlett  was  largely  self-sterile,  this  self-sterility  occurring 
entirely  too  often  to  justify  an  orchardist  in  attempting  to  grow 
pears  without  providing  for  cross-pollination  (fig.  4). 

The  "Winter  Nelis  has  proved  to  be  the  best  pollinizer  for  the 
Bartlett.     Although  all  the  other  varieties  tested  proved  to  be  satis- 


Bulletin  373] 


PEAR  POLLINATION 


15 


factory  pollinizers,  preference  should  possibly  be  given  to  Winter 
Nelis,  Bosc,  Cornice,  and  Anjou  in  the  order  named. 

Table  6  presents  the  results  of  an  experiment  designed  to  show, 
from  the  average  yield  of  two  comparable  orchards,  the  benefits  to  be 
derived  from  cross-pollination.     The   orchard  of  P.   M.  Beaser  of 

TABLE  5 
Bartlett  Pear  Pollination  in  Sierra  Nevada  Foothills 


1918 

1919 

1922 

1923 

Number 
blossoms 
counted 

Per 

cent 
set 

Number 
blossoms 
counted 

Per 

cent 
set 

Number 
blossoms 
counted 

Per 
cent 
set 

Number 
blossoms 
counted 

Per 
cent 
set 

Bartlett 

Normal  Set.. 
xSelf 

2916 
918 
518 
426 

459 
414 

19.5 
1.3* 
18.7 
20.6 

15.4 
20.1 

2583 
398 
377 
396 

310 
407 

3.8 
16.0 
18.8 
27.2 

19.3 
21.8 

1732 
634 
517 
500 
532 
429 
496 
530 
452 

2.7 
0.1 
1.9 
1.8 
4.8 
2.3 
3.0 
3.9 
5.1 

3026 
926 

612 
546 

893 

7.2 
0.0 

xAnjou 

xBosc 

xComice 

xEaster 

xHovey 

xHowell 

xW.  Nelis .... 

11.0 
13.0 

14.0 

♦Fruit  small. 


BARTLETT   PEAR   POLLI/i AT  10/15 

5ierra  Nevada  Poothifl  Locations  ~-  Grass  Valley  1918  - 1919  ~  192  2  "1923 


Gross 


Percent  of  Blossoms  Maturing 

1318  1319  19ZZ.  1923 


/Formal  5e.t 

x5ele 

xA/ijov; 

xBosc 

xComice 

xEaster 

xhovEy 

xHi/iter  /SELI5 


■■■__■ I B 

HH  _  BKBI  I ■■___ 

■ ■■_ 

SB       I 

■■■___■■■■_■ 

■BH I L ■»_ 


Fig.  4. — This  chart  shows  the  influence  of  various  kinds  of  pollen  when 
applied  to  the  flowers  of  the  Bartlett  pear  under  Sierra  Nevada  Foothill 
locations.    Note  the  failure  of  the  trees  to  set  fruit  when  self -pollinated. 


16 


UNIVERSITY    OF    CALIFORNIA EXPERIMENT    STATION 


Chicago  Park,  Nevada  County,  consists  of  a  solid  block  of  one  thousand 
Bartlett  pear  trees,  no  provision  having  been  made  for  cross-polli- 
nation. These  trees  are  perhaps  twenty-five  years  old.  There  is 
located  on  the  Loma  Rica  Ranch,  some  eight  miles  away,  a  small 
block  of  old  Bartlett  trees  of  about  the  same  age  and  vigor  as  those 
on  the  Beaser  place.  Many  of  these  trees  had,  however,  during  the 
six  or  eight  years  previous  to  1918,  been  topworked  to  other  varieties. 
AVith  the  exception  of  the  presence  of  pollinating  varieties  close  at 
hand  on  the  Loma  Rica  Ranch,  the  two  orchards  just  described  were 
in  all  respects  comparable.    Both  orchards  bloomed  profusely  in  1918. 

TABLE  6 

Comparison  of  Yield  on  Bartlett  Trees  in  Nevada  County  with  and 
without  Pollinating  Varieties,  1918. 


With  Pollinating  Varieties 

Without  Pollinating  Varieties 

Number 
blossoms 
counted 

Per 
cent 

set 

Average  yield 
per  tree  in 
packed  boxes 

Number 
blossoms 
counted 

Per 
cent 
set 

Average  yield 

per  tree  in 
packed  boxes 

3007 

14.9 

2.19 

3170 

6.0 

.77 

The  figures  show  that  the  trees  provided  with  cross-pollination 
produced  a  crop  almost  three  times  as  great  as  that  produced  by  the 
trees  which  did  not  receive  cross-pollination.  It  should  also  be  noted 
that  the  favorable  showing  for  the  trees  receiving  cross-pollination  was 
made  in  spite  of  the  fact  that  this  orchard  lost  much  of  its  fruit  as  a 
result  of  the  ravages  of  pear  blight. 


POLLINATION  EEQUIEEMENTS  OF  CEETAIN  PEAE  YAEIETIES 
OTHEE  THAN  THE  BAETLETT 

A.  Interior  Valley  Conditions 

Some  twenty-five  pear  varieties  have  been  tested  as  to  their 
pollination  requirements  when  grown  under  interior  valley  conditions. 
These  experiments  were  conducted  in  the  University  Farm  orchards 
at  Davis.  The  major  portion  of  this  work  consisted  of  the  determi- 
nation of  normal  sets  and  the  testing  of  the  varieties  for  self -sterility 
or  self-fertility.  A  few  cross-pollinations  were  made  between  some  of 
the  varieties.  Tests  have  been  conducted  for  from  one  to  four  years. 
The  results  of  this  work  are  presented  in  table  7. 


Bulletin  373] 


PEAR  POLLINATION 


17 


TABLE  7 

Pollination  of  Pear  Varieties  Other  than  Bartlett 

University  Farm,  Davis,  1919,  1920,  1922,  1923 


1919 

1920 

1922 

1923 

Variety 

Number 
counted 

Per 
cent 
set 

Number 
counted 

Per 
cent 

set 

Number 
counted 

Per 
cent 
set 

Number 
counted 

Per 
cent 

set 

Alencon 

Normal  Set 

249 
79 

254 

227 

172 
193 

512 
451 

499 
433 

17.3 
6.1 

26.1 
0.0 

23.8 
2.1 

15.4 
13.1 

15.2 
5.3 

990 
511 

881 
293 

724 
335 

843 
576 

246 
265 

839 
307 

530 

288 

736 
300 

498 
302 

727 
811 

122 

168 

0.0 
0.0 

0.1 
0.0 

7.0 
0.6 

7.7 
0.3 

12.0 
0.1 

5.9 
0.0 

14.0 
0.6 

7.4 
0.0 

0.9 
0.0 

7.0 
6.0 

2.4 
0.0 

314 
559 

240 
483 

183 
710 

306 

427 

757 
432 

214 

340 
161 

884 
581 

1.2 
0.0 

10.0 
6.4 

7.1 
20.4 

13.4 
0.0 

5.5 
0.0 

0.0 

2.3 
1.2 

3.9 
0.3 

900 

272 
179 

1313 

374 
232 
358 

1326 
342 

1643 

548 

1549 
260 

1759 
392 

xSelf 

Angouleme 

Normal  Set 

xSelf 

Anjou 

Normal  Set 

xSelf 

Bloodgood 

Normal  Set 

xSelf 

Bosc 

Normal  Set 

48.6 

xSelf 

xComice 

63.2 

xEaster 

29.6 

B.  S.  Fox 

Normal  Set 

xSelf 

Clairgeau 

Normal  Set 

15.7 

xSelf 

7.3 

xComice 

14.5 

xW.  Nelis 

Clapp  Favorite 

Normal  Set 

10.6 

8.7 

xSelf 

2.6 

Col.  Wilder 

Normal  Set 

20.3 

xSelf 

6.0 

Comet 

Normal  Set 

xSelf 

Cornice 

Normal  Set 

19.9 

xSelf 

6.5 

D.  Hovey 

Normal  Set 

19.5 

xSelf 

11.7 

18  UNIVERSITY   OF   CALIFORNIA EXPERIMENT   STATION 

TABLE  7— (Continued) 


Variety 


1919 


Number 
counted 


Per 
cent 
set 


1920 


Number 
counted 


Per 

cent 
set 


1922 


Number 
counted 


Per 

cent 
set 


1923 


Number 
counted 


Per 
cent 
set 


Easter 

Normal  Set 

xSelf 

Flemish  Beauty 

Normal  Set 

xSelf 

Forelle 

Normal  Set 

Self 

Gifford 

Normal  Set 

xSelf 

Glout  Morceau 

Normal  Set 

xSelf 

Hardy- 
Normal  Set 

xSelf 

xComice 

xEaster 

Howell 

Normal  Set 

xSelf 

Kieffer 

Normal  Set 

xSelf >, 

LeConte 

Normal  Set 

xSelf 

P.  Barry 

Normal  Set 

xSelf 

Madeline 

Normal  Set 

xSelf 

Seckel 

Normal  Set 

xSelf 

Winter  Nelis 

Normal  Set 

xSelf 

xSelf  G.V.f 

Cornice 

*  Per  cent  set  estimated 


403 


317 

442 


957 
463 

385 
165 

900 
209 


57 
195 

1048 
442 


8.7 


13.6 
9.3 


6.8 
3.5 

4.9 
5.5 

7.5 
0.0 


63.2 
4.6 

12.4 
0.0 


799 
275 


608 
315 

501 

274 

538 
307 

701 

227 


673 

277 

640 

278 

457 
557 

938 
311 


516 
307 

804 
238 
341 


4.0 
0.7 


10.0 
0.0 

14.0 
0.0 

3.9 
0.6 

8.5 
7.5 


0.6 
0.3 

8.2 
0.0 

14.0 
0.0 

7.9 
0.9 


22.0 
3.0 

6.0 
0.0 
0.0 


376 
356 

142 

226 

258 
472 

710 
117 

239 
276 

752 
530 


64 
407 

441 
551 

1528 
329 

301 
474 

1003 
151 


579 


4.0 
0.8 

18.2 
6.2 

25.2 
0.0 

10.3 

2.7 

3.4 
2.1 

3.5 
0.3 


2.0 
4.4 

14.9 
0.2 

3.6 
0.0 

8.3 
0.8 

8.1 
0.0 

15.0s 
0.0 


1601 
317 


1555 

441 
381 


1414 
267 


1628 
319 


533 
423 

108 
1464 

764 


3.7 

6.3 


3.8 

4.7 
14.7 


7.1 
0.0 


11.5 

2.8 


77.5 
19.8 

6.7 
0.2 

16.5 


t  Pollen  from  Grass  Valley. 


Bulletin  373] 


PEAR  POLLINATION 


19 


In  order  to  summarize  the  results  presented  in  table  7,  the  writers 
have  segregated  the  varieties  into  three  groups  as  follows : 


Self-Sterile 

Self-Fertile 

Doubtful 

Variety 

Years 
tested 

Variety 

Years 
tested 

Variety 

Number 
years 
self- 
fertile 

Number 
years 
self- 
sterile 

Alencon 

2 
2 
1 
1 
2 
3 
1 
3 

Cornice 

4 
1 
3 
3 

Angouleme 

1 

2 
1 
1 

2 
2 
1 
1 

1 
1 
1 
3 
1 

Bloodgood 

1 

B.  S.  Fox 

Flemish  Beauty.. 

Hardy 

Howell 

Anjou 

1 

Comet 

Bosc 

1 

Forelle 

Clapp  Favorite  . . 
Clairgeau 

1 

Le  Conte 

2 

Madeline.... 

Col.  Wilder 

2 

Winter  Nelis 

Dana  Hovey 

Easter 

Gifford 

G.  Morceau 

Kieffer 

2 
2 

1 
1 
4 

P.  Barry 

2 

Seckel 

1 

Those  varieties  listed  as  self -sterile  must  be  provided  with  some 
other  variety  to  pollinate  them. 

While  the  self -fertile  varieties  may  be  expected  to  produce  good 
crops  without  pollinizers,  it  should  be  noted  from  the  table  that  in  no 
case  did  the  self-pollinations  equal  the  normal  set.  The  advantage 
of  cross-pollination  is  thus  clearly  shown  since  these  trees  are  located 
in  a  variety  orchard,  where  abundant  opportunity  for  cross-polli- 
nation is  afforded. 

The  doubtful  varieties  are  those  which  have  not  behaved  con- 
sistently from  year  to  year.  For  instance,  the  Anjou  was  self -fertile 
in  1919  and  1922,  but  largely  self -sterile  in  1920,  and  the  Clairgeau 
was  self -fertile  two  years  and  practically  self -sterile  two  years.  It 
would  be  inadvisable  to  plant  these  doubtful  varieties  in  solid  blocks, 
as  there  would  be  too  many  years  when  they  would  be  self -sterile  or 
practically  so,  and  would  not  produce  paying  crops.  Only  a  few  cross- 
pollinations  have  been  made  with  these  varieties  but  in  each  case  a 
very  satisfactory  set  has  been  obtained. 


20 


UNIVERSITY    OF    CALIFORNIA EXPERIMENT    STATION 


B.  Coastal  Conditions 

Experiments  under  coastal  conditions  have  been  rather  limited, 
consisting  of  one  year 's  trial  in  the  Santa  Clara  Valley  and  work  with 
one  variety  in  Sonoma  County.  The  results  of  this  work  are  presented 
in  table  8.  TABLE  g 

Pollination  of  Pear  Varieties  Other  than  Bartlett 
Coastal  Conditions 


1920 

1922 

Variety 

Number  of 
blossoms 
counted 

Number 
set 

Per  cent 
set 

Number  of 
blossoms 
counted 

Number 
set 

Per  cent 
set 

Bosc 

Normal  Set , 

xSelf 

1987 
410 

1901 
422 
205 

1758 
425 
327 
304 

2000 
486 

2000 

892 

353 

40 

2108 
404 
299 
308 

1237 
531 

1025 
532 

2000 
486 
342 
315 
231 

527 

82 

92 
0 
3 

71 
4 
2 

91 

99 
55 

123 

75 

54 

6 

73 

5 

81 

110 

15 

0 

32 

8 

218 

7 

59 

52 

19 

26 
20 

4.8 
0.0 
1.4 

4.0 

0.9 

0.6 

29.9 

4.4 
11.3 

6.1 

8.4 

15.0 

12.0 

3.4 

1.2 

27.0 

35.7 

1.2 
0.0 

3.1 

1.5 

10.0 

1.4 

17.0 

16.0 

8.0 

1793 

485 
220 

81 

1 

31 

Clairgeau 

Normal  Set 

xSelf 

xForelle 

Cornice 

Normal  Set 

xSelf 

xHowell 

xW.  Nelis 

Easter 

Normal  Set 

xSelf 

Glout  Morceau 

Normal  Set 

xSelf 

xEaster 

xW.  Nelis 

Hardy 

Normal  Set 

xSelf 

xComice 

xW.  Nelis 

Howell 

Normal  Set 

xSelf 

Winter  Seckel 

Normal  Set 

xSelf 

Winter  Nelis 
Normal  Set.. 

4.5 

xSelf    

0.2 

xBartlett 

14.0 

xEaster 

xGlout  Morceau 

Bulletin  373]  PEAR  pollination  21 

From  the  preceding  table  it  will  be  noted  that  Clairgeau,  Cornice, 
Howell,  Hardy,  and  Winter  Nelis  proved  to  be  self -sterile  or  prac- 
tically so.    Bosc,  Easter,  and  Glout  Morceau  are  self-fertile. 

Although  Winter  Seckel  produced  considerable  fruits  when  self- 
pollinated,  it  has  been  classified  as  partially  self -sterile.  Since  the  set 
from  self-pollinations  was  low  when  compared  with  the  normal  set, 
the  writers  believe  that  this  variety  should  not  be  planted  in  solid 
blocks. 

C.  Sierra  Nevada  Foothill  Conditions 

Experiments  were  conducted  under  foothill  conditions  during  the 
years  1919,  1922,  and  1923.  The  results  of  this  work  are  presented 
in  table  9. 

A  study  of  table  9  shows  Anjou,  Cornice,  D.  Hovey,  and  P.  Barry 
to  be  self -sterile  or  practically  so.  Bosc  may  be  classed  as  doubtful 
since  it  was  sterile  one  year  and  partially  self-sterile  the  other.  The 
one  season's  results  indicate  that  Easter  is  self -fertile. 

It  is  interesting  to  note  that  in  all  cases  the  Bartlett  has  proved 
to  be  a  satisfactory  pollenizer.  With  the  exception  of  Winter  Nelis 
X  Bosc  and  the  reciprocal  cross,  pollinations  with  Bartlett  have  given 
the  highest  yields.  With  the  exception  of  Dana  Hovey  X  Bartlett, 
all  crosses  made  have  increased  the  set  over  that  obtained  by  the 
normal  count,  and  in  most  cases  the  resultant  set  was  two  or  three 
times  as  much  as  that  produced  under  field  conditions. 

Reimer9  observes  in  southern  Oregon  that  the  Bartlett  is  not  a 
good  pollinizer  for  Anjou  and  also  that  a  satisfactory  pollinizer  for 
the  Cornice  is  yet  to  be  found.  The  writers  feel  that  the  conflict 
between  Oregon  observations  and  the  results  obtained  in  California 
are  perhaps  due  to  climatic  factors. 

From  the  preceding  discussion  it  seems  reasonable  to  draw  the 
following  conclusions :  Under  Sierra  Nevada  foothill  conditions  all 
pear  varieties  should  be  considered  as  self-sterile — meaning  that  it  is 
inadvisable  to  plant  pears  without  provisions  for  cross-pollination. 
The  Bartlett  can  be  considered  as  a  satisfactory  pollinizer  for  other 
varieties. 

INFLUENCE   OF  CROSS  POLLINATION  UPON  THE   JUNE  DROP 

Table  10  gives  in  detail  the  results  of  certain  experiments  con- 
ducted in  the  orchards  of  the  Vaca  Valley  Ranch  of  the  Earl  Fruit 
Company  at  Vacaville  during  the  season  of  1918  (figs.  5  to  10, 
inclusive).  This  orchard  consists  of  a  solid  block  of  Bartletts,  no 
provision  having  been  made  for  cross-pollination. 

»  Reimer,  F.  C,  Better  Fruit,  vol.  XVIII,  Nov.  6,  1923. 


22 


UNIVERSITY   OF    CALIFORNIA — EXPERIMENT   STATION 


TABLE  9 

Pollination  of  Pear  Varieties  Other  than  Baetlett 
Sierra  Nevada  Foothill  Conditions 


1919 

1922 

1923 

Variety 

Number 
of 
blos- 
soms 

counted 

Number 
set 

Per 
cent 
set 

Number 
of 
blos- 
soms 

counted 

Number 
set 

Per 
cent 
set 

Number 
of 
blos- 
soms 

counted 

Number 
set 

Per 
cent 
set 

Anjou 

Normal  Set... 
xSelf 

1747 
311 
218 

300 

1258 
148 
120 

1048 
274 
226 

1713 
376 
330 

1559 
387 

352 

51 

0 

32 

28 

156 
0 
3 

55 

9 

15 

11 

5 
37 

53 

2 

11 

2.8 

0.0 

14.6 

9.3 

12.4 
0.0 
2.5 

5.2 
3.0 
6.6 

0.6 

1.3 

11.2 

3.3 
0.5 

3.1 

2170 
476 
386 
364 

2062 
521 
474 
341 

2188 
770 
495 
477 
551 
566 

2391 

370 

477 
442 
340 
408 

89 

0 

27 

21 

94 
11 
22 
27 

0 

0 

10 

20 

10 

0 

29 

22 

48 
42 
23 
38 

4.1 

0.0 
7.0 
5.7 

4.5 
2.1 
4.6 
7.9 

0.0 
0.0 
2.0 
4.2 
1.8 
0.0 

1.2 

5.9 
10.0 
9.2 
6.7 
9.3 

1398 
527 
392 
290 

2958 
1110 

552 
479 
629 

2537 
551 

534 
534 
465 

56 

0 

35 

27 

110 
6 

51 
42 
75 

259 

1 

85 

146 

54 

xBartlett 

xBosc 

xHowell 

Bosc 

Normal  Set.... 
xSelf 

4.0 
0.0 

xBartlett 

xW.  Nelis 

Cornice 

Normal  Set.... 
[xSelf 

8.5 
9.3 

3.7 
0.5 

xAnjou 

xBartlett 

xBosc 

9.2 
8.9 

xW.  Nelis 

D.  Hovey 

Normal  Set.... 

xSelf 

xBartlett 

Easter 

Normal  Set.... 

xSelf 

11.9 

xBartlett 

P.  Barry 

Normal  Set.... 
xSelf 

xBartlett 

Winter  Nelis 
Normal  Set.... 
xSelf 

10.0 
0.0 

xAnjou 

xBartlett 

xBosc 

15.9 
27.3 

xComice 

11.6 

xEaster 

Bulletin  373] 


PEAR   POLLINATION 


23 


Fig.  5. — A  typical  example  of  the  normal  set  in  the  Vaea  Valley  Eanch 
orchards,  1918.  Two  pears  matured  from  seventeen  blossoms — a  11.7  per  cent  set. 
In  years  of  normal  bloom  a  10  per  cent  set  would  assure  a  satisfactory  crop. 


24 


UNIVERSITY    OF    CALIFORNIA EXPERIMENT    STATION 


Fig.  6. — Two  Bartlett  pears  set  from  eight  blossoms  pollinated  with  Bartlett 
pollen.  A  typical  cluster  of  this  variety  when  self -pollinated.  Vaca  Valley 
Ranch,  1918. 


Bulletin  373" 


PEAK   POLLINATION 


25 


Fig.  7. — Five  Bartlett  pears  set  from  twelve  blossoms  pollinated  with  Cornice 
pollen.  A  typical  cluster  resulting  from  crossing  Bartlett  with  Cornice.  Vaca 
Valley  Ranch,  1918. 


26 


UNIVERSITY    OF    CALIFORNIA EXPERIMENT    STATION 


Fig.  8. — Four  Bartlett  pears  set  from  seventeen  blossoms  pollinated  with 
Easter  pollen.  A  typical  cluster  resulting  from  crossing  Bartlett  with  Easter. 
Vaca  Valley  Ranch,  1918. 


Bulletin  373] 


PEAR   POLLINATION 


27 


Fig.  9. — Eleven  Bartlett  pears  set  from  twenty-five  blossoms  pollinated  with 
Howell  pollen.  A  typical  cluster  resulting  from  crossing  Bartlett  with  Howell. 
Vaca  Valley  Ranch,  1918. 


28 


UNIVERSITY    OF    CALIFORNIA EXPERIMENT    STATION 


Fig.  10. — Ten  Bartlett  pears  set  from  twenty  blossoms  pollinated  with  Winter 
Nelis  pollen.  A  typical  cluster  resulting  from  crossing  Bartlett  with  Winter 
^elis.    Yaca  Valley  Ranch,  1918. 


Bulletin  373 


PEAR   POLLINATION 


29 


Fig.  11. — Bartlett  pears  (left),  self-pollinated  (right),  cross-pollinated  with 
Winter  Nelis.  Showing  the  characteristic  shape  of  each  and.  the  relative  amount 
of  core  tissue. 


30 


UNIVERSITY   OF    CALIFORNIA EXPERIMENT   STATION 


It  is  unfortunate  that  the  normal  set  count  of  the  fruits  matured 
could  not  be  secured.  The  branches  on  which  these  records  were  made 
received  the  customary  hand  thinning  early  in  the  summer  and 
therefore  later  counts  would  not  have  been  reliable. 

TABLE  10 

Pollination  of  the  Bartlett,  1918 

Vaca  Valley  Eanch,  Vacaville 


Variety 

Number  of 

blossoms 

counted 

Number 
set 

Per  cent 
apparently 
set  May  10 

Number 

fruits 
matured 

Per 

cent 
matured 

Bartlett 

Normal  Set 

1276 
424 
278 
308 
238 
256 

108 
79 
90 
86 
63 
75 

8.4 

18.6 
32.3 
27.9 
26.4 
29.2 

41 

73 
71 

47 
60 

xSelf 

9.7 

xComice 

xEaster 

26.3 
23.1 

xHowell 

19.8 

xWinter  Nelis 

23.4 

Those  flowers  which  were  self -pollinated  matured  a  much  smaller 
crop  than  did  those  which  were  crossed  with  pollen  from  other 
varieties.  It  is  interesting  to  note  from  the  above  table  that  the  loss 
from  the  June  drop  of  those  fruits  resulting  from  cross-pollination 
amounted  to  only  20  per  cent,  while  with  those  self -pollinated  the 
loss  was  48  per  cent.  This  would  seem  to  indicate  that  fewer  pears 
will  be  lost  at  the  June  drop  if  adequate  provision  is  made  for  cross- 
pollination. 

Inasmuch  as  the  resulting  set  in  this  orchard  when  the  blossoms 
actually  received  their  own  pollen  was  more  than  double  the  normal 
set,  it  seems  clear  that  the  provision  of  some  agency,  preferably  honey 
bees,  for  the  transfer  of  pollen  from  flower  to  flower  would  be  highly 
profitable. 


INFLUENCE  OF  CROSS  POLLINATION  UPON  MATURITY,  SHAPE, 
QUALITY,  PRODUCTION  AND  KEEPING  PERIOD 

Blanchard10  observes  that:  "In  the  Antelope  Valley  Bartlett  pears 
resulting  from  cross-pollinated  flowers  mature  their  fruit  from  two  to 
three  weeks  earlier  than  those  fruits  resulting  from  self-pollination. 
There  is  also  a  marked  increase  in  the  yields  from  orchards  having 
pollinating  varieties  present. ' ' 

10  Blanchard,  V.  F.,  Unpublished  data,  Los  Angeles  County,  1923. 


Bulletin  373]  PEAR  pollination  31 

Overholser  and  Latimer11  report  that:  ''The  flavor  of  cross- 
pollinated  pears  from  the  Antelope  Valley  was  richer,  but  had  only 
about  three-fourths  as  much  edible  flesh  as  the  self -pollinated  fruit, 
because  of  the  amount  of  tissue  comprising  the  core  of  the  former. 
The  characteristic  shape  of  the  self -pollinated  Bartlett  pear  is  different 
from  the  cross-pollinated  pear  (fig.  11).  There  was  little  apparent 
difference  in  the  length  of  the  keeping  period  between  the  self- 
pollinated  and  cross-pollinated    Bartlett  and  Winter  Nelis." 

The  writers  do  not  know  of  any  other  section  where  the  self- 
pollinated  Bartlett  behaves  as  it  does  in  the  Antelope  Valley,  but 
certainly  under  those  conditions  it  is  highly  desirable  to  provide  for 
cross-pollination. 

Another  variety  where  cross-pollination  is  highly  desirable  is  in  the 
case  of  the  Glout  Morceau,  which  generally  produces  irregular  shaped 
fruits  when  self-pollinated. 


EECOMMENDATIONS 

From  a  study  of  the  experimental  data  presented  and  from  the 
observations  and  experiments  of  many  orchardists  of  the  state,  the 
conclusion  is  inevitable  that  pear  orchards  should  in  general  be 
provided  with  facilities  for  cross-pollination. 

Since  the  Bartlett  is  the  most  important  variety  grown  in  the  state 
at  the  present  time,  the  question  at  once  arises  as  to  what  variety  shall 
be  selected  as  a  pollinizer  for  it.  For  foothill  locations  where  the 
bulk  of  the  crop  is  offered  for  "green"  shipment,  this  question  is 
probably  not  difficult  to  answer.  Tn  these  places,  the  Anjou,  Bosc, 
Cornice,  Howell,  and  Winter  Nelis  are  all  excellent  pears,  bringing 
prices  equal  to  or  better  than  the  Bartlett  for  eastern  shipment.  These 
varieties  may  not  give  an  equal  tonnage  with  the  Bartlett,  but  they 
are  all  fair  producers.  The  Cornice  should  be  avoided  in  windy 
locations,  since  its  skin  is  quite  delicate  and  mars  most  easily. 

In  valley  locations  the  question  of  providing  cross-pollination  for 
the  Bartlett  is  more  difficult.  The  grower  must  concede  that  where 
the  set  can  be  increased  100  per  cent  or  more  by  the  planting  of  one 
pollinating  tree  to  every  eight  Bartletts,  the  returns  per  acre  will 
still  be  greatly  increased  even  though  the  fruit  of  the  pollinating 
variety  may  have  little  or  no  commercial  value.  Although  there  has 
been  no  thorough  attempt  to  test  the  adaptability  of  various  varieties 
to  different  locations,  the  writers  believe  from  the  information  in  hand 

ii  Overholser,  E.  L.,  and  Latimer,  L.  P.,  Calif.  Agr.  Exp.  Sta.  Ann.  Kept., 
p.  130,  1922. 


32  UNIVERSITY    OF    CALIFORNIA EXPERIMENT    STATION 

that  the  Winter  Nelis  will  prove,  from  all  standpoints,  to  be  the  most 
efficient  pollinizer  for  the  Bartlett  when  grown  under  valley  con- 
ditions. Cornice,  Bosc,  Easter,  and  Hardy  also  have  given  satisfactory 
results  and  are  recommended  in  the  order  named. 

Where  dried  fruit  is  a  primary  product  and  where  the  fruit  of  the 
pollinizer  for  the  Bartlett  must  also  be  dried,  special  difficulties  are 
presented.  No  experiments  have  as  yet  been  conducted  in  this  state 
to  determine  the  drying  qualities  of  the  various  varieties.  In  order 
to  avoid  the  use  of  artificial  evaporators,  the  pollinizer  must  ripen 
its  fruit  at  about  the  same  time  or  shortly  after  the  Bartlett.  Practi- 
cally all  dried  pears  in  California  are  sundried.  Keeping  especially 
in  mind  the  time  of  ripening,  the  Howell  and  Hardy  varieties  seem 
to  be  the  best  pollinizers  for  the  Bartlett  where  the  entire  crop  is  to 
be  dried. 

Under  coastal  conditions  Winter  Nelis  and  Cornice  should  prove 
to  be  the  most  efficient  pollenizers  for  the  Bartlett. 

Although  comparatively  few  cross-pollinations  have  been  made  on 
varieties  other  than  the  Bartlett,  the  writers  feel  from  the  data  pre- 
sented that  the  Bartlett  may  be  successfully  used  as  a  general 
pollinizer.  This  is  especially  true  of  the  more  important  sorts,  such 
as  Anjou,  Bosc,  Cornice,  Hardy,  Howell,  Easter,  and  Winter  Nelis. 


POLLINATING  AGENCIES 

After  planting  inter-fertile  varieties,  the  orchardist  should  by  all 
means  provide  an  agency  for  the  transfer  of  the  pollen  from  the  trees 
of  one  variety  to  those  of  another.  The  common  honey  bee  is  by  far 
the  best  carrier  of  pollen:  it  will  pay  the  grower  to  keep  bees  even 
though  he  may  not  care  to  go  into  the  honey  business.  Bees,  however, 
are  a  very  profitable  side  line  for  the  orchardist,  especially  if  alfalfa 
fields  are  available  to  work  on  after  the  blooming  season  of  fruit  has 
passed.  About  one  hive  of  bees  to  an  acre  of  bearing  orchard  should 
be  provided.  Preferably  the  hives  should  be  scattered  as  widely  as 
possible  throughout  the  orchard  during  the  blooming  season.  Experi- 
ments and  experience  have  shown  that  little  reliance  can  be  placed  on 
wind  and  insects,  other  than  the  honey  bee,  in  effecting  the  transfer 
of  pollen  from  tree  to  tree  or,  in  fact,  from  flower  to  flower. 

Gossard  and  Walton12  show  that  under  Ohio  conditions,  pear 
blossoms  which  have  been  pollinated  for  72  hours  are  not  likely  to 

12  Gossard,  H.  A.,  and  Walton,  R.  C,  Dissemination  of  Fire  Blight,  Ohio  Agr. 
Exp.  Sta.  Bull.  357,  1922. 


Bulletin  373]  PEAR  pollination  33 

be  inoculated  with  pear  blight  and  that  susceptibility  to  the  disease 
does  not  exist  in  blossoms  that  have  been  pollinated  for  144  hours. 

These  writers  infer  that  the  presence  of  numerous  honey  bees  in 
an  orchard  at  blossoming  time  will  insure  a  good  crop  of  fruit  by 
bringing  about  the  pollination  of  each  flower  as  soon  as  it  unfolds, 
thus  rendering  a  majority  of  the  bloom  non-susceptible  to  blight 
before  the  disease  is  generally  diffused  over  the  orchard. 

The  relation  of  bees  to  the  spread  of  pear  blight  under  California 
conditions  is  a  question  which  requires  additional  investigation.  The 
work  in  Ohio  would  seem  to  indicate  that  numerous  bees  in  the  orchard 
early  in  the  season  would  be  an  advantage  in  restricting  the  ' '  blossom 
blight, ' '  in  addition  to  their  necessity  as  pollinating  agents. 

Eliminating  from  consideration  all  conditions  which  may  influence 
the  fruitfulness  of  an  orchard  except  those  occurring  at  the  blossom 
period,  it  may  be  said  that  the  set  is  largely  influenced  by  weather 
conditions  at  that  time.  Cold  weather,  aside  from  killing  the  blossoms 
or  lowering  the  vitality  of  the  pollen,  often  prevents  bees  from  work- 
ing. The  same  is  true  if  cloudy,  wet.  and  windy  weather  prevails. 
For  their  best  work  bees  demand  clear,  warm,  and  quiet  days,  and 
since  the  weather  at  the  time  of  bloom  is  often  quite  unsettled,  it  is 
readily  seen  that  the  blossoming  period  of  the  various  pollinating 
varieties  should  overlap  perhaps  a  week  in  order  that  there  may  be 
one  or  two  days  at  least  when  the  weather  will  be  favorable  for 
insect  pollination. 


ARRANGEMENT  OF  THE  ORCHARD  FROM  A  POLLINATION 
STANDPOINT 

In  planting  an  orchard  it  is  desirable  to  have  at  least  every  sixth 
and  preferably  every  fourth  row  of  a  pollinating  variety.  For  con- 
venience in  the  management  of  the  orchard,  it  is  best  to  plant  two 
rows  of  one  kind,  then  two  rows  of  the  pollinating  variety,  and  so  on ; 
or,  if  it  is  desired  to  have  more  of  one  varietj^  than  another,  four  rows 
of  the  favorite  variety,  then  two  rows  of  the  pollinizer,  and  repeat. 
For  one  reason  or  another,  it  is  often  desirable  to  reduce  the  number 
of  pollinating  trees  to  the  minimum.  Under  these  circumstances,  one 
tree  in  twenty-five  is  perhaps  sufficient,  although  at  least  one  tree  in 
eight  is  strongly  recommended.  It  is  seldom  wise  to  graft  over  a 
part  of  a  tree  to  the  pollinating  variety  as  this  tends  toward  confusion 
and  added  expense  in  harvesting. 


34 


UNIVERSITY   OF    CALIFORNIA EXPERIMENT   STATION 


In  planting  one  tree  of  the  pollinizer  to  seven  or  eight  of  the  main 
variety,  the  former  should  be  placed  as  every  third  tree  in  every 
third  row  in  such  a  way  that  the  spaces  in  the  pollinating  rows  are 
broken  as  indicated  in  the  diagram,  the  '  *  0 r '  in  each  case  representing 
a  pollinating  tree. 

0  .  .  0 


If  by  chance  a  self -sterile  variety  has  been  planted  in  a  solid  block, 
the  necessary  pollinizer  may  be  introduced  by  grafting.  Some  relief 
may  be  obtained  during  the  years  while  waiting  for  the  trees  grafted 
over  to  pollinating  varieties  to  come  into  bearing,  by  cutting  off  large 
limbs  of  pollinating  varieties,  placing  the  cut  ends  in  buckets  of  water 
and  distributing  them  throughout  the  orchard  during  the  blooming 
period.  Such  limbs  will  live  for  several  days  and  continue  to  bloom, 
forming  pollen  for  the  bees  to  transfer  to  the  self -sterile  variety. 


SUMMARY  OF  PEAR  POLLINATION 

1.  A  12  per  cent  cane  sugar  solution  gave  during  the  seasons  of 
1916,  1917,  1918,  1919,  1920,  1922,  and  1923,  an  entirely  satisfactory 
artificial  germination  of  pear  pollen. 

2.  There  is  comparatively  little  variation  in  the  amount  of  pollen 
produced  by  various  pear  varieties.  Pollen  production  is  always 
abundant. 

3.  The  blooming  period  of  most  pears  is  comparatively  short. 

4.  With  the  exception  of  several  of  the  earliest  and  latest  bloomers 
all  pear  varieties  overlap  in  their  period  of  bloom. 

5.  Bartlett  is  to  a  limited  extent  self -sterile  under  interior  valley 
and  coastal  conditions.  Under  Sierra  Nevada  foothill  conditions  it  is 
almost  entirely  self -sterile  (at  least  in  certain  years)  and  therefore 
should  not  be  planted  without  pollinizers. 


Bulletin  373]  PEAR  POLLINATION  35 

6.  Winter  Nelis  has  proved  to  be  the  best  pollinizer  for  the 
Bartlett  under  all  conditions  tested. 

7.  Under  valley  conditions,  the  Cornice,  Bosc,  and  Hardy  have 
proved  to  be  satisfactory  pollinizers  for  the  Bartlett.  Howell, 
Angouleme,  Anjou,  and  Forelle  have  also  given  fair  results. 

8.  Under  coastal  conditions,  Cornice,  Clairgeau,  and  Easter  proved 
satisfactory  as  pollinizers  for  the  Bartlett. 

9.  Under  Sierra  Nevada  foothill  conditions,  Bosc,  Cornice,  Anjou, 
Easter,  D.  Hovey,  and  Howell  are  recommended  as  pollinizers  for  the 
Bartlett  in  the  order  named. 

10.  Winter  Nelis  has  been  largely  self -sterile  under  all  conditions 
tested  but  may  be  successfully  pollinated  with  the  Bartlett. 

11.  Alencon,  Bloodgood,  B.  S.  Fox,  Comet,  Forelle,  LeConte,  and 
Madeline  have  proved  to  be  almost  entirely  self-sterile  under  valley 
conditions. 

12.  Cornice,  Flemish  Beauty,  Hardy,  and  Howell  may  be  classed 
as  self -fertile  under  valley  conditions. 

13.  Angouleme,  Anjou,  Bosc,  Clapp  Favorite,  Clairgeau,  Col. 
Wilder,  Dana  Hovey,  Easter,  Gifford,  Glout  Morceau,  Kieffer,  P. 
Barry,  and  Seckel  may  be  considered  doubtful,  and  the  writers  would 
not  recommend  that  they  be  planted  under  valley  conditions  without 
provisions  for  cross-pollination. 

14.  Under  coastal  conditions.  Clairgeau,  Cornice,  Howell,  and 
Hardy  are  almost  self -sterile. 

15.  Bosc,  Easter,  and  Clout  Morceau  are  fairly  self -fertile  under 
coastal  conditions. 

16.  Anjou,  Bosc,  Cornice,  D.  Hovey,  and  P.  Barry  should  be  con- 
sidered self -sterile  under  foothill  conditions. 

17.  Easter  may  perhaps  be  classed  as  self-fertile  under  foothill 
conditions;  however,  attention  is  here  drawn  to  the  fact  that  in  the 
case  of  this  variety  only  one  season 's  results  are  available. 

18.  Pear  fruits  resulting  from  cross-pollination  do  not  appear  to 
exhibit  the  same  tendency  to  fall  after  the  June  drop  as  do  those 
resulting  from  self-pollination. 

19.  Pollinating  agencies  such  as  honey  bees  are  necessary  to  set  a 
good  crop  of  fruit. 

20.  One  stand  of  bees  should  be  provided  for  each  acre  of  orchard. 

21.  Care  should  be  taken  in  the  arrangement  of  varieties  in  the 
orchard  to  facilitate  cross-pollination  and  convenience  in  orchard 
management. 


36  UNIVERSITY    OF    CALIFORNIA EXPERIMENT    STATION 


A  CKNOWLEDGMENTS 

The  writers  wish  to  express  their  appreciation  of  the  help  they 
have  received  from  the  following  persons  in  carrying  out  this  work: 
Messrs.  M.  N.  Wood,  0.  Lilleland,  M.  J.  Heppner,  R.  Peckham ;  J.  L. 
Stahl ;  Misses  R.  M.  Amesbury  and  Edna  Russ  and  to  several  advanced 
students  in  Pomology  who  rendered  assistance  in  the  field  and 
laboratory.  Dr.  W.  L.  Howard  has  given  service  in  suggestions  and 
criticisms. 

The  Earl  Fruit  Company.  Mr.  A.  L.  Wisker  of  the  Loma  Rica 
Ranch,  Mr.  P.  M.  Beaser  of  Chicago  Park,  Mr.  V.  T.  McCurdy,  and 
Mr.  F.  Wilcox  of  Santa  Clara  Valley,  and  Mr.  Don  Searby  of  Sonoma 
County  have  kindly  allowed  the  use  of  their  orchards  for  certain 
experiments  and  have  at  all  times  shown  a  kindly  and  cooperative- 
interest  in  the  work. 


8m-3,'24. 


